1. Field of the Invention
The present invention relates to a semiconductor light emitting device (such as a light emitting diode or a laser diode) employing a group III nitride semiconductor.
2. Description of Related Art
Group III nitride semiconductors are group III-V semiconductors employing nitrogen as a group V element, and typical examples thereof include aluminum nitride (AlN), gallium nitride (GaN) and indium nitride (InN), which can be generally expressed as AlxInyGa1-x-yN (0≦x≦1, 0≦y≦1 and 0≦x+y≦1).
A method of manufacturing a nitride semiconductor by growing a group III nitride semiconductor on a gallium nitride (GaN) substrate having a major surface defined by a c-plane by metal organic chemical vapor deposition (MOCVD) is known in general. This method is so applied that a GaN semiconductor multilayer structure having an n-type layer and a p-type layer can be formed, and a light emitting device can be prepared using such a multilayer structure. Such a light emitting device can be utilized as a light source for a backlight for a liquid crystal panel, for example.
A major surface of a GaN semiconductor regrown on a GaN substrate having a major surface defined by a c-plane is also defined by the c-plane. Light extracted from the c-plane is randomly polarized (unpolarized). When incident upon the liquid crystal panel, therefore, light other than specific polarized light corresponding to an incidence-side polarizing plate is blocked, and does not contribute to brightness to an emission side. Therefore, it is difficult to implement high brightness display (efficiency is 50% at the maximum).
In order to solve this problem, a technique of preparing a light emitting device by growing a GaN semiconductor having a major surface defined by a plane other than the c-plane, i.e., a nonpolar plane such as an a-plane or an m-plane or a semipolar plane is discussed. When a light emitting device having a p-type layered portion and an n-type layered portion is formed by a GaN semiconductor layer having a major surface defined by a nonpolar plane or a semipolar plane, strongly polarized light can be emitted. Therefore, loss on the incidence-side polarizing plate can be reduced by matching a direction of polarization of the light emitting device and a direction of passage polarization of the incidence-side polarizing plate of the liquid crystal panel with each other. Consequently, high brightness display can be implemented.